The long-term goal of our research program is to elucidate microRNA mechanisms that alter normal regulation of genes in response to overactivity of the angiotensin II type 1 receptor (AT1R). Angiotensin II (AngII) is the classical mediator of the effects of the renin-angiotensin system on the cardiovascular homeostasis. This receptor regulates gene expression targeted by the AT1R-blockers (ARB), a widely used class of anti- hypertensive drugs that are currently in trial for the prevention of vascular, renal and cardiac hypertrophy, aortic aneurism, vascular fibrosis, breast tumor growth and angiogenesis. Inhibition of AT1R in renal, vascular and cardiac cells by ARBs is protective, but the activation o the receptor causes hypertrophy and progressive fibrosis of the respective organs/tissues. In preliminary studies we have discovered that chronic activation of AT1R deregulates gene expression through both transcriptional and post-transcriptional mechanisms. To directly link deregulation of gene expression to hypertrophy and fibrosis, we profiled mRNA and microRNA (miRNA) expression in the AT1R TG mice aorta, heart, and in HL1-AT1R (cardiomyocyte) and the VSMC-AT1R cell lines. Typical transcriptional and miRNA regulatory mechanisms are significantly altered in all of the experimental models. In a separate study, we have shown significantly altered miRNA expression profile in dilated cardiomyopathy human hearts. The altered miRNAs target gene networks that do account for compensatory remodeling in human heart failure. These novel studies suggest that mRNA and miRNA profiles, together, contribute to AT1R biology in health and disease. Our current proposal will focus on the novel roles of two AT1R-modulated microRNAs: miR-205 and mir-483. Three Specific Aims are proposed to test the hypothesis that specific transcriptional and post-transcriptional regulatory mechanisms tilt the dynamics of typical hypertrophy and fibrosis signaling towards a disease connotation. They are: (i) to determine miR-205 mechanisms which alter critical signaling components in models of hypertrophy and fibrosis, (ii) to determine the miR-483 mechanism of up-regulation of the rennin angiotensin system, and (iii) to determine the AT1R regulated mechanisms of biogenesis and the stability of miR-205 and miR-483. If the AT1R activity is not regulated properly, AngII stimulus becomes chronic and can damage the tissue, as well as contribute to chronic disorders of blood vessels, kidney and heart. A clear understanding of these mechanisms is important to improve the therapeutic application of ARBs. These proposed studies will advance our knowledge of the biology of AT1R signaling causing hypertrophy and fibrosis. There is potential relevance for this knowledge base in understanding normal functioning aorta, vasculature in brain, kidney and heart, as well as the pathology of heart failure, atherosclerosis and aortic aneurysm.